Intervertebral spinal inserts are used to provide support and maintain normal distance between adjacent vertebrae in cases where a patient's vertebral discs have degenerated. Such degeneration can occur as a result of aging or trauma and typically results in pinched or damaged nerves between or proximal to the adjacent vertebrae. Moreover, such discal degeneration causes shifting of the loading along the patient's spinal column, which in turn further accelerates the vertebral degeneration.
Intervertebral inserts are typically used to reestablish normal intervertebral spacing, stabilize and reduce bone motion and, in conjunction with graft matter, to cause fusion between adjacent vertebral bodies.
A common problem with existing intervertebral inserts is that their insertion into the patient's spine is usually accomplished by invasive open surgical procedures. Such invasive surgery can be performed by entering either through the patient's back or through the abdomen. A major disadvantage of such invasive surgery is that it requires a considerable post-operative recovery time for the patient.
Another disadvantage is that, during such major surgery, the actual insertion of the intervertebral insert requires distraction of the adjacent vertebrae to first open a sufficiently large passage for the insertion of the insert therebetween. Such distraction is typically performed by dedicated instrumentation and invasive tools which must first enter the intervertebral space and then grip and hold apart the adjacent vertebrae.
A related disadvantage of current surgical methods of inserting intervertebral inserts is that they require cutting through, scarring and damaging either the posterior longitudinal ligament or the anterior longitudinal ligament, the facet joint capsules, interspinous ligaments and other paraspinal tissues. This reduces the amount of natural tension between the relevant vertebrae which reduces spinal column stability and may allow the inserts to move from their desired location.
An additional problem with the insertion of current intervertebral inserts is the requirement that portions of the adjacent vertebrae have to be drilled, chiseled away or otherwise removed to accommodate the particular geometric shape and orientation of the insert. Accordingly, in addition to the requirement of distracting the adjacent vertebrae, current systems typically also require drilling or chiseling away of the hard exterior surface of the vertebral endplates so that the insert can be received therein. This removal of the hard exterior endplate surface exposes the softer cancellous bone which is not sufficiently strong to bear the required load. Accordingly, the subsequent insertion of a typical metal cage-type insert into this softer cancellous portion of the vertebral bone requires the spinal load to be directed against a weaker supporting surface. A danger exists that such inserts may fail in their purpose of maintaining intervertebral spacing because they sink into softer bone.
Moreover, the shape of current inserts does not take advantage of the natural contoured shape of the adjacent vertebral surfaces such that an intervertebral insert can be provided which supports itself flush against the contour of the vertebral surfaces with the vertebrae being supported at a proper lordotic angle.
An additional problem with many current insert designs is that they often do not adequately promote or provide an opportunity for bone growth therethrough so as to firmly embed the insert within the spine over time.